- For post radiation therapy patients: the nadir reference value (#1) is the last PSA measured before increases are documented, with subsequent values obtained a minimum of 1 week apart; if the PSA at time point 3 (value #3A) is greater than that at point 2, then eligibility has been met; if the PSA is not greater than point 2 (value #3B), but value #4 is, the patient is eligible assuming that other criteria are met and if values 3A or #4 are 2.0 ng/mL or more above the nadir reference value (#1) according to Phoenix/American Society for Therapeutic Radiology and Oncology (ASTRO) criteria